(1) Field of the Invention
The present invention relates to a butterfly valve in which the shaft connecting the butterfly disk consists of double or single eccentric structure.
(2) Description of the Prior Art
In general, a butterfly valve, as shown in FIG. 13 and FIG. 14 illustrating a sectional view along the line X--X (horizontal direction) of FIG. 13, opens or closes the through-hole 4 of the ring-shaped housing 1 by installing the shaft 2 consisting of double eccentric structure on the housing 1 perpendicularly to the tube axis 10, securing the butterfly disk 3 to the shaft 2, and flapping the butterfly disk 3 like a butterfly thorough rotation of the shaft 2.
The seat ring 5 is installed on the inner periphery of the through-hole 4, which is held by the fitting recess 6 of the housing 1 and the seat holding ring 7. The contact surface 8 between the inner periphery of the seat ring 5 and the outer periphery of the butterfly disk 3 is formed to be a circular arc having a slight taper as shown in FIG. 15, forming the circular locus 9 with the radius R1 centering around the point 0 where the circular locus 9 of the circular arc intersects the center line 10 of the butterfly disk 3. The shape of the contact surface of the butterfly disk 3 is not restricted to the example in FIG. 15. There are also the shapes of a complete circular cone as shown in FIG. 16 and the shape in which the radius R2 of the circular arc is small, R2LR1, as shown in FIG. 17.
Though the following is the description of the example in FIG. 15, the description can also be applied to the examples in FIGS. 16 and 17.
The double eccentric structure of the shaft 2 is defined as the structure in which the shaft 2 has the eccentricity 11a equal to the distance "d1" from the central contact surface 11 of the butterfly disk 3 (primary eccentricity) and the eccentricity 10a equal to the distance d2 from the tube axis 10 of the point 0 (secondary eccentricity).
Though the following is the description of the case in which the central point of the shaft 2 consists of double eccentric structure, the description can also be applied to the so-called single eccentric structure with the eccentricity of "d1" (primary eccentricity) and free from double eccentricity (d2=0).
When the shaft 2 having the above double eccentricity rotates, the contact points A an B of the butterfly disk 3 rotates along the lock (a1-A-a2) and (b1-B-b2) shown by the continuous line different from the circular locus 9. That is, when the closed butterfly disk 3 opens, the contact point A rotates while slightly shifting from the point A to the point a2 and the contact point B rotates while slightly shifting from the point B to the point b2 toward the inside of the locus 9. Therefore, the contact points A and B of the butterfly disk 3 do not cause unnecessary sliding because they are diagonally separated from the seat ring 5 without sliding on it. When the opened butterfly disk 3 closes, the contact points A and B contact at the intersections A and B with the circular locus 9 before they shift from the contact points a2 and b2 toward the outside points a1 and b1 contact points A an B so that they will cross each other. Therefore, the bearing pressure of the butterfly disk 3 increases and airtightness is improved. However, if rotation becomes excessive after contacting at the points A and B, the torque excessively increases and the seat ring damages. Therefore, a stopper is normally installed to control rotation.
The butterfly valve consisting of the above double eccentric structure smoothly opens or closes and the airtightness is improved. However, it has the following disadvantages. That is, when the butterfly disk 3 opens or closes, the effect of double eccentric structure is remarkably shown around the side portions A and B shown in the top view of FIG. 14. However, because the butterfly disk 3 rotates while contacting with the seat ring 5 around the top and bottom contact points C and D of the butterfly disk 3, there is a problem that abnormal scratches shown by the hatched are 12 in FIGS. 13 and 14 are produced at the top and bottom contact points C and D of the butterfly disk 3 and the seat ring 5 locally abrades to decrease the sealing effect.
U.S. Pat. No. 3,957,073 shows the description that "Peripheral portions on each side of the vane 53 are shaved adjacent the pin position to accommodate for the thickness to the vane 53 when it moves toward closed positions". However, the description does not include how the cut portion contacts the seat ring and the problem is left that it is unknown whether or not a long term sealing effect can be obtained.
It is the first object of the present invention to provide a butterfly valve capable of obtaining stable sealing effect for a long time by minimizing scratches of the butterfly disk and abrasion of the seat ring.
Other objects and features of the present invention will be clarified by the following description.